Regenerative medicine is benefiting from recent advances relating to the isolation, culture, and use of various types of progenitor cells. This disclosure provides further improvements for the commercial development of human pluripotent stem cells and their derivatives.
Embryonic stem cells have two very special properties: First, unlike other normal mammalian cell types, they can be propagated in culture almost indefinitely, providing a virtually unlimited supply. Second, they can be used to generate a variety of tissue types of interest as a source of replacement cells and tissues for use in tissue therapy, or for use in the screening of pharmaceutical agents.
Thomson et al. (U.S. Pat. No. 5,843,780; Proc. Natl. Acad. Sci. USA 92:7844, 1995) were the first to successfully isolate and propagate pluripotent stem cells from primates. They subsequently derived human embryonic stem (hES) cell lines from human blastocysts (Science 282:114, 1998). Gearhart and coworkers derived human embryonic germ (hEG) cell lines from fetal gonadal tissue (Shamblott et al., Proc. Natl. Acad. Sci. USA 95:13726, 1998; and U.S. Pat. No. 6,090,622). Both hES and hEG cells have the long-sought characteristics of pluripotent stem cells: they can be cultured extensively without differentiating, they have a normal karyotype, and they are capable of producing a number of important cell types.
A significant challenge to the use of pluripotent stem cells for therapy is that they are traditionally cultured on a layer of feeder cells to prevent differentiation (U.S. Pat. No. 5,843,780; U.S. Pat. No. 6,090,622). According to Thomson et al. (Science 282:114, 1998), hPS cells cultured without feeders soon die, or differentiate into a heterogeneous population of committed cells. Leukemia inhibitory factor (LIF) inhibits differentiation of mouse ES cells, but it does not replace the role of feeder cells in preventing differentiation of human ES cells.
U.S. Pat. No. 6,800,480 (Geron Corp.) is entitled Methods and materials for the growth of primate-derived primordial stem cells. International Patent Publication WO 01/51616 (Geron Corp.) is entitled Techniques for growth and differentiation of human pluripotent stem cells. An article by Xu et al. (Nature Biotechnology 19:971, 2001) is entitled Feeder-free growth of undifferentiated human embryonic stem cells. An article by Lebkowski et al. (Cancer J. 7 Suppl. 2:S83, 2001) is entitled Human embryonic stem cells: culture, differentiation, and genetic modification for regenerative medicine applications. International Patent Publication WO 03/020920 is entitled Culture System for Rapid Expansion of Human Embryonic Stem Cells. An article by Li et al. (Biotechnology and Bioengineering, Published Online: 21 Jun. 2005) is entitled Expansion of human embryonic stem cells. These publications report exemplary culture reagents and techniques for propagating embryonic stem cells in an undifferentiated state, and their use in preparing cells for human therapy.
The information provided in the section below further advances the science of hES cell culture that will facilitate growing and manipulating undifferentiated pluripotent stem cells, and help realize the full commercial potential of embryonic cell therapy.